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Diy optical pickup for guitar -- is it possible?

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sorveltaja:
After testing several kinds of circuits found on the net, considering sine wave(amplified output from the receiver) to square wave conversion, it doesn't seem to be that straightforward. 

One of them being a zero crossing detector, that, as I assumed, should be sensitive enough for the purpose:
 

But there wasn't any output at all. So I removed all the parts from the breadboard, just in case, that there was mistakes, and built it again from the scratch. Still the same result.

Next thing was to test with multimeter, does the 'preamp' -circuit(mentioned in previous post) give measurable 'peaks', as the electromagnetic pickup does, when the string is plucked.

No, it didn't. Be it AC or DC range. Nothing. But the output is still there, when connected to the laptop's mic input. Somehow it sounds stronger, when compared to the 'high output', dual coil electromagnetic pickup.

If there isn't measurable AC or DC values, then what kind of output is it anyways?

russ57:
The first thing to check is the frequency range of the multi meter.
Secondly, the meter will measure the 'rms' value of the signal, this is the average value, not the peak. And it probably assumes a sine wave.
If your signal is a series of 'spikes' rather than a sine wave, then the rms value could be very low.
Audio design really needs an oscilloscope. You can pick one ok for audio off any Chinese trading site if not eBay for under aud50. £20?
(Turning a sine wave to square is easy. Just apply massive gain) .

Russ



Russ

sorveltaja:
Russ, yes I've been searching for the oscilloscope for a while now. Maybe something like the Nano DSO series, with colour screen.
Some of them even have two channels, like SainSmart Mini ARM DSO202 Nano.

Most of them on the Ebay are located in China, which means that the delivery times tend to be rather long. So I'll probably pick one of the few ones located in Europe.

I'm tempted to go and buy a full size, entry level Rigol, which seems to be quite popular. But perhaps it's not a time for going that far yet.

What comes to my description of the signal of the plucked string, when measured from the electromagnetic pickup's output, it was incorrect.

It actually isn't in a form of spike(s), but more like an envelope.

I'll probably butcher the subject by trying to explain it, but the first picture on this page hopefully shows, what I mean by the envelope: http://www.muzique.com/lab/pick.htm

PekkaNF:
I really would recomed entry level oscilloscope. Even old analog would be whole lot better than without one. I have had one old CRT 10MHz model that I bought 20€ and gave away, it would have been fine for this.

New DSO:s maybe easier to use, they normally can "find" the wave form with a push button. If you have nothing connected or no signal you normally find mains frequency or quantisizing noise.....but that is learning curve.

With low level audio signal you can't even blow up the scope, when you mess with grounds.....normal scopes have only one ground = chassis, this ir nice to acknowledge.

I had Rigol 1052 (old model several years, sold it with 250€), I think, New owner has been really happy with it. I bought Rigol DS2102E, somewhere bit over 600€ that time with serial decode etc. I wanted bigger display and some triggering options.

https://www.batronix.com/shop/oscilloscopes/DSO.html
https://www.batterfly.com/shop/

They offer few times a year free upgrades of software features, like triggering and decoders (if you are into serial protocols etc.)

Discrete devices with their own displays, settings and ergometrics are just so much nicer to use than the boxes that need a laptop and weird ground (trough the laptop?).

Pekka

sorveltaja:
This post is an off-topic, but sort of related, because it considers the recommended kind of measuring device, oscilloscope.

After pondering, and watching countless amount of Youtube review videos about oscilloscopes(mostly EEVblog's, and also reading his forum),
I came to the conclusion, that the desktop one could offer a lot more functions and options, than I could ever need or fully understand.

One thing, that I must say: This kind of project (optical pickup for the guitar) definitely does not require a fancy 'full-featured' desktop oscilloscope, for the experimenter to observe signals.

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Totally off-topic:

When I'm talking about having a desktop oscilloscope, it's more like a part of my own journey, as I have wanted to have one for years now.

Then came the question: which brands are available in finnish stores? Owon's cheapest model(SDS1022) has nice, big 7 inch screen in it, but for some reason, there isn't too many reviews to be found of that online, so the reputation isn't confirmed in any way.

After all, Rigol is the one, that I ordered. As Pekka said "..but that is learning curve". Probably a steep one, that holds true for me, when I get that device in my clumsy paws.
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Back to the original subject. As Russ mentioned, 'Turning a sine wave to square is easy. Just apply massive gain'. But how much gain can one apply to a single op-amp, without making it self-oscillating? Or is it something, that requires multiple stages?

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